In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until translucent.
Stir in the minced garlic and cook for an additional 1 minute until fragrant.
Add the zucchini, yellow squash, and red bell pepper to the pot. Sauté for 5-7 minutes until the vegetables begin to soften.
Mix in the corn, green beans, diced tomatoes (with their juice), oregano, basil, salt, and pepper.
Pour in the vegetable broth and bring the mixture to a boil.
Reduce the heat to low, cover the pot, and let it simmer for 20-25 minutes, stirring occasionally, until all the vegetables are tender.
Taste and adjust seasoning if necessary. Serve hot, garnished with fresh parsley if desired.